Retrospective Cohort Study of Outcomes for Neonates and Infants Undergoing Inguinal Hernia Surgery at Multiple Australian and New Zealand Hospitals: The RetroNeo Study.

Statistical Analysis

Author

Dr Benjamin Moran, MBBS, BMedSci (Hons), MMedStats, FCICM, FANZCA

Published

October 22, 2024

1 Introduction

This is the statistical analysis that accompanies the RetroNeo study, which examines the anaesthetic techniques and perioperative outcomes of neonates and infants undergoing inguinal hernia surgery.

2 Results

2.1 Demographics

Characteristic

Overall
N = 524

1

Age Categories at Birth

≤ 27 Weeks
N = 49

1

28-32 Weeks
N = 116

1

33-36 Weeks
N = 123

1

≥36 Weeks
N = 236

1
Number of Patients (N) 524 49 116 123 236
Post-Menstrual Age at Birth in Weeks (Median (IQR)) 36.1 (31.4, 38.4) 26.0 (24.7, 26.6) 30.1 (28.7, 31.6) 35.3 (34.0, 36.0) 38.7 (38.0, 40.0)
Male Sex (N (%)) 440 (84%) 45 (92%) 97 (84%) 105 (85%) 193 (82%)
Weight at Birth in Grams (Median (IQR)) 2,140 (1,159, 2,998) 731 (600, 910) 1,203 (935, 1,650) 2,108 (1,800, 2,520) 3,140 (2,600, 3,450)
Location Prior to Day of Surgery




    Home/Residential Care 353 (68%) 12 (25%) 60 (52%) 89 (73%) 192 (82%)
    Hospital Ward 63 (12%) 4 (8.3%) 12 (10%) 17 (14%) 30 (13%)
    NICU 46 (8.9%) 20 (42%) 20 (17%) 4 (3.3%) 2 (0.9%)
    PICU 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
    Special Care Nursery 26 (5.0%) 6 (13%) 15 (13%) 5 (4.1%) 0 (0%)
    Other Health Care Facility 31 (6.0%) 6 (13%) 9 (7.8%) 7 (5.7%) 9 (3.9%)
Respiratory Support Prior to Surgery




    LFNP 37 (76%) 20 (74%) 13 (76%) 3 (75%) 1 (100%)
    HFNP 6 (12%) 2 (7.4%) 3 (18%) 1 (25%) 0 (0%)
    NIV 1 (2.0%) 0 (0%) 1 (5.9%) 0 (0%) 0 (0%)
    ETT 5 (10%) 5 (19%) 0 (0%) 0 (0%) 0 (0%)
NICU Admission Between Birth & Surgery 238 (46%) 48 (98%) 102 (88%) 53 (44%) 35 (15%)

Medical History

Intrauterine Growth Restriction (IUGR) 112 (22%) 15 (31%) 46 (40%) 29 (24%) 22 (9.4%)
Intraventricular Haemorrhage (IVH) 24 (4.6%) 16 (33%) 7 (6.0%) 0 (0%) 1 (0.4%)
Retinopathy of Prematurity 62 (12%) 34 (69%) 27 (23%) 1 (0.8%) 0 (0%)
Congenital Cardiac Disease 56 (11%) 21 (43%) 22 (19%) 7 (5.8%) 6 (2.6%)
Chronic Lung Disease 98 (19%) 44 (90%) 45 (39%) 6 (5.0%) 3 (1.3%)
History of Apnoea (Any Aetiology) 120 (23%) 37 (76%) 65 (56%) 13 (11%) 5 (2.1%)
History of Invasive Ventilation 104 (20%) 40 (82%) 48 (41%) 8 (6.6%) 8 (3.4%)
Respiratory Support at Surgery 49 (9.4%) 27 (55%) 17 (15%) 4 (3.3%) 1 (0.4%)
History of Caffeine Use 122 (23%) 36 (73%) 76 (66%) 10 (8.3%) 0 (0%)
1

n; Median (Q1, Q3); n (%)

2.2 Surgical Details

Characteristic

Overall
N = 519

1

Age Categories at Birth

≤ 27 Weeks
N = 48

1

28-32 Weeks
N = 116

1

33-36 Weeks
N = 122

1

≥36 Weeks
N = 233

1
Number of Patients (N) 519 48 116 122 233
Post-Menstrual Age at Birth in Weeks (Median (IQR)) 36.1 (31.4, 38.3) 25.9 (24.5, 26.6) 30.1 (28.7, 31.6) 35.3 (34.0, 36.0) 38.7 (38.0, 40.0)
Post-Menstrual Age at Surgery in Weeks (Median (IQR)) 44.9 (41.4, 48.1) 41.1 (39.2, 44.1) 41.1 (38.4, 43.5) 44.8 (41.9, 47.9) 47.0 (44.9, 50.1)
Weight at Birth in Grams (Median (IQR)) 2,140 (1,150, 2,998) 731 (600, 910) 1,203 (935, 1,650) 2,109 (1,800, 2,540) 3,130 (2,600, 3,450)
Weight at Surgery in Grams (Median (IQR)) 4,200 (3,300, 5,205) 3,565 (3,015, 3,990) 3,108 (2,630, 3,700) 3,960 (3,190, 5,115) 4,900 (4,260, 5,600)
Type of Hernia Repair




    Bilateral 218 (42%) 31 (65%) 71 (61%) 47 (39%) 69 (30%)
    Unilateral 301 (58%) 17 (35%) 45 (39%) 75 (61%) 164 (70%)
Surgical Approach




    Laparoscopic 23 (4.4%) 2 (4.2%) 4 (3.4%) 6 (4.9%) 11 (4.7%)
    Open 496 (96%) 46 (96%) 112 (97%) 116 (95%) 222 (95%)
Incarcerated Hernia 36 (6.9%) 1 (2.1%) 7 (6.0%) 8 (6.6%) 20 (8.6%)
Additional Associated Procedure 55 (11%) 8 (17%) 12 (10%) 13 (11%) 22 (9.4%)
Total Duration in Minutes (Median (IQR)) 74 (59, 94) 97 (74, 122) 79 (61, 103) 73 (59, 88) 70 (56, 85)
Anaesthetic Duration in Minutes (Median (IQR)) 71 (55, 91) 93 (70, 115) 74 (57, 100) 69 (53, 85) 69 (54, 83)
Surgical Duration in Minutes (Median (IQR)) 34 (25, 47) 50 (36, 67) 37 (28, 53) 32 (22, 43) 31 (25, 44)
1

n; Median (Q1, Q3); n (%)

2.3 Anaesthetic Details

2.3.1 General Anaesthesia

Characteristic

Overall
N = 519

1

Age Categories at Birth

≤ 27 Weeks
N = 48

1

28-32 Weeks
N = 116

1

33-36 Weeks
N = 122

1

≥36 Weeks
N = 233

1
Number of Patients (N) 519 48 116 122 233
Anaesthetic Type




    GA Only 163 (33%) 13 (28%) 29 (27%) 40 (34%) 81 (36%)
    Spinal Only 77 (15%) 7 (15%) 27 (25%) 22 (18%) 21 (9.4%)
    Caudal Only 1 (0.2%) 0 (0%) 1 (0.9%) 0 (0%) 0 (0%)
    GA + Spinal 4 (0.8%) 0 (0%) 3 (2.8%) 0 (0%) 1 (0.4%)
    GA + Caudal 221 (44%) 21 (46%) 40 (37%) 51 (43%) 109 (49%)
    GA + Sedation 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
    Spinal + Sedation 8 (1.6%) 2 (4.3%) 2 (1.8%) 1 (0.8%) 3 (1.3%)
    Caudal + Sedation 18 (3.6%) 3 (6.5%) 5 (4.6%) 5 (4.2%) 5 (2.2%)
    GA + Spinal + Caudal 1 (0.2%) 0 (0%) 1 (0.9%) 0 (0%) 0 (0%)
    GA + Caudal + Sedation 5 (1.0%) 0 (0%) 1 (0.9%) 0 (0%) 4 (1.8%)
Type of GA




    Sevoflurane 260 (50%) 24 (50%) 49 (42%) 61 (50%) 126 (54%)
    Propofol 7 (1.3%) 0 (0%) 2 (1.7%) 3 (2.5%) 2 (0.9%)
    Sevoflurane + NO2 46 (8.9%) 4 (8.3%) 11 (9.5%) 9 (7.4%) 22 (9.4%)
    Sevoflurane + Propofol 82 (16%) 5 (10%) 12 (10%) 16 (13%) 49 (21%)
    Sevoflurane + Dexmedetomidine 6 (1.2%) 0 (0%) 1 (0.9%) 3 (2.5%) 2 (0.9%)
    Sevoflurane + Propofol + Dexmedetomidine 4 (0.8%) 1 (2.1%) 2 (1.7%) 1 (0.8%) 0 (0%)
    Propofol + NO2 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
    Propofol + Dexmedetomidine 2 (0.4%) 0 (0%) 0 (0%) 0 (0%) 2 (0.9%)
    None 112 (22%) 14 (29%) 39 (34%) 29 (24%) 30 (13%)
Type of NMBA




    Rocuronium 54 (10%) 12 (25%) 14 (12%) 10 (8.2%) 18 (7.7%)
    Vecuronium 58 (11%) 6 (13%) 14 (12%) 11 (9.0%) 27 (12%)
    Atracurium 92 (18%) 8 (17%) 18 (16%) 23 (19%) 43 (18%)
    Cisatracurium 19 (3.7%) 1 (2.1%) 5 (4.3%) 7 (5.7%) 6 (2.6%)
    Suxamethonium 5 (1.0%) 0 (0%) 1 (0.9%) 1 (0.8%) 3 (1.3%)
    Suxamethonium + Rocuronium 1 (0.2%) 1 (2.1%) 0 (0%) 0 (0%) 0 (0%)
    Suxamethonium + Vecuronium 1 (0.2%) 0 (0%) 0 (0%) 1 (0.8%) 0 (0%)
    Suxamethonium + Atracurium 3 (0.6%) 1 (2.1%) 0 (0%) 1 (0.8%) 1 (0.4%)
    Suxamethonium + Cisatracurium 1 (0.2%) 0 (0%) 1 (0.9%) 0 (0%) 0 (0%)
    None 285 (55%) 19 (40%) 63 (54%) 68 (56%) 135 (58%)
NMBA Reversal Agent




    Sugammadex 116 (22%) 6 (13%) 22 (19%) 34 (28%) 54 (23%)
    Neostigmine 65 (13%) 10 (21%) 15 (13%) 14 (11%) 26 (11%)
    None 338 (65%) 32 (67%) 79 (68%) 74 (61%) 153 (66%)
Paracetramol 219 (42%) 24 (50%) 37 (32%) 54 (44%) 104 (45%)
Parecoxib 7 (1.3%) 0 (0%) 0 (0%) 3 (2.5%) 4 (1.7%)
Opioid 147 (28%) 15 (31%) 22 (19%) 27 (22%) 83 (36%)
Dexmedetomidine 1 (0.2%) 0 (0%) 0 (0%) 0 (0%) 1 (0.4%)
Type of Airway




    ETT 339 (65%) 29 (60%) 69 (59%) 82 (67%) 159 (68%)
    LMA 49 (9.4%) 2 (4.2%) 5 (4.3%) 8 (6.6%) 34 (15%)
    Anaesthetic Face Mask 6 (1.2%) 1 (2.1%) 1 (0.9%) 1 (0.8%) 3 (1.3%)
    HFNP 10 (1.9%) 1 (2.1%) 5 (4.3%) 1 (0.8%) 3 (1.3%)
    Hudson Mask 3 (0.6%) 0 (0%) 1 (0.9%) 1 (0.8%) 1 (0.4%)
    LFNP 19 (3.7%) 8 (17%) 3 (2.6%) 5 (4.1%) 3 (1.3%)
    Guedel 3 (0.6%) 0 (0%) 0 (0%) 1 (0.8%) 2 (0.9%)
    Chin Support 1 (0.2%) 0 (0%) 0 (0%) 0 (0%) 1 (0.4%)
    None 89 (17%) 7 (15%) 32 (28%) 23 (19%) 27 (12%)
1

n; n (%)

2.3.2 Spinal Anaesthesia

Characteristic

Overall
N = 90

1

Age Categories at Birth

≤ 27 Weeks
N = 9

1

28-32 Weeks
N = 33

1

33-36 Weeks
N = 23

1

≥36 Weeks
N = 25

1
Number of Patients (N) 90 9 33 23 25
Spinal Local Anaesthetic (Drug (Concentration))




    Bupivacaine 0.25% 2 (2.2%) 1 (11%) 1 (3.0%) 0 (0%) 0 (0%)
    Bupivacaine 0.5% 39 (43%) 6 (67%) 15 (45%) 10 (43%) 8 (32%)
    Levobupivacaine 0.5% 36 (40%) 2 (22%) 11 (33%) 9 (39%) 14 (56%)
    Levobupivacaine 0.7% 1 (1.1%) 0 (0%) 1 (3.0%) 0 (0%) 0 (0%)
    Ropivacaine 0.2% 1 (1.1%) 0 (0%) 1 (3.0%) 0 (0%) 0 (0%)
    None 11 (12%) 0 (0%) 4 (12%) 4 (17%) 3 (12%)
Number of Attempts




    1 56 (64%) 6 (67%) 21 (64%) 14 (64%) 15 (63%)
    2 20 (23%) 1 (11%) 7 (21%) 5 (23%) 7 (29%)
    3 8 (9.1%) 2 (22%) 4 (12%) 1 (4.5%) 1 (4.2%)
    4 4 (4.5%) 0 (0%) 1 (3.0%) 2 (9.1%) 1 (4.2%)
Complications




    Bleeding 1 (4.2%) 0 (NA%) 0 (0%) 1 (14%) 0 (0%)
    Failed Attempt 15 (63%) 0 (NA%) 7 (64%) 3 (43%) 5 (83%)
    Inadequate Block 5 (21%) 0 (NA%) 2 (18%) 2 (29%) 1 (17%)
    Inadequate Block Duration 2 (8.3%) 0 (NA%) 2 (18%) 0 (0%) 0 (0%)
    Inadequate Surgical Conditions 1 (4.2%) 0 (NA%) 0 (0%) 1 (14%) 0 (0%)
Conversion to GA 22 (24%) 1 (11%) 9 (27%) 5 (22%) 7 (28%)
Adjuvant Sedation Used 8 (8.9%) 2 (22%) 2 (6.1%) 1 (4.3%) 3 (12%)
Propofol Sedation 1 (1.1%) 0 (0%) 0 (0%) 1 (4.3%) 0 (0%)
Dexmedetomidine Sedation 1 (1.1%) 1 (11%) 0 (0%) 0 (0%) 0 (0%)
Midazolam Sedation 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
Clonidine Sedation 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
Remifentanil 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
Ketamine Sedation 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
NO2 Sedation 2 (2.2%) 0 (0%) 2 (6.1%) 0 (0%) 0 (0%)
Sucrose Sedation 4 (4.4%) 1 (11%) 0 (0%) 0 (0%) 3 (12%)
Type of Airway




    ETT 1 (1.1%) 0 (0%) 1 (3.0%) 0 (0%) 0 (0%)
    LMA 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
    Anaesthetic Face Mask 2 (2.2%) 0 (0%) 1 (3.0%) 0 (0%) 1 (4.0%)
    HFNP 2 (2.2%) 0 (0%) 2 (6.1%) 0 (0%) 0 (0%)
    Hudson Mask 1 (1.1%) 0 (0%) 0 (0%) 1 (4.3%) 0 (0%)
    LFNP 8 (8.9%) 5 (56%) 1 (3.0%) 1 (4.3%) 1 (4.0%)
    Guedel 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
    Chin Support 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
    None 76 (84%) 4 (44%) 28 (85%) 21 (91%) 23 (92%)
1

n; n (%)

2.3.3 Caudal Anaesthesia

Characteristic

Overall
N = 246

1

Age Categories at Birth

≤ 27 Weeks
N = 24

1

28-32 Weeks
N = 48

1

33-36 Weeks
N = 56

1

≥36 Weeks
N = 118

1
Number of Patients (N) 246 24 48 56 118
Spinal Local Anaesthetic (Drug (Concentration))




    Bupivacaine 0.25% 27 (11%) 4 (17%) 6 (13%) 5 (8.9%) 12 (10%)
    Bupivacaine 0.5% 1 (0.4%) 0 (0%) 0 (0%) 0 (0%) 1 (0.9%)
    Levobupivacaine 0.2% 3 (1.2%) 0 (0%) 1 (2.1%) 1 (1.8%) 1 (0.9%)
    Levobupivacaine 0.25% 43 (18%) 3 (13%) 4 (8.5%) 13 (23%) 23 (20%)
    Ropivacaine 0.1% 1 (0.4%) 0 (0%) 0 (0%) 0 (0%) 1 (0.9%)
    Ropivacaine 0.2% 159 (65%) 16 (67%) 34 (72%) 36 (64%) 73 (63%)
    Ropivacaine 0.3% 1 (0.4%) 0 (0%) 1 (2.1%) 0 (0%) 0 (0%)
    None 8 (3.3%) 1 (4.2%) 1 (2.1%) 1 (1.8%) 5 (4.3%)
Caudal Additives




    Adrenaline 15 (42%) 3 (60%) 2 (40%) 3 (33%) 7 (41%)
    Clonidine 18 (50%) 1 (20%) 3 (60%) 5 (56%) 9 (53%)
    Dexmedetomidine 1 (2.8%) 1 (20%) 0 (0%) 0 (0%) 0 (0%)
    Saline 2 (5.6%) 0 (0%) 0 (0%) 1 (11%) 1 (5.9%)
Number of Attempts




    1 191 (79%) 20 (83%) 39 (81%) 39 (71%) 93 (82%)
    2 39 (16%) 2 (8.3%) 9 (19%) 12 (22%) 16 (14%)
    3 9 (3.7%) 1 (4.2%) 0 (0%) 4 (7.3%) 4 (3.5%)
    4 2 (0.8%) 1 (4.2%) 0 (0%) 0 (0%) 1 (0.9%)
Complications




    Failed Attempt 10 (100%) 3 (100%) 0 (NA%) 4 (100%) 3 (100%)
Conversion to GA 3 (1.2%) 1 (4.2%) 0 (0%) 1 (1.8%) 1 (0.8%)
Adjuvant Sedation Used 23 (9.3%) 3 (13%) 6 (13%) 5 (8.9%) 9 (7.6%)
Propofol Sedation 15 (6.1%) 2 (8.3%) 4 (8.3%) 3 (5.4%) 6 (5.1%)
Dexmedetomidine Sedation 17 (6.9%) 3 (13%) 5 (10%) 4 (7.1%) 5 (4.2%)
Midazolam Sedation 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
Clonidine Sedation 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
Remifentanil 1 (0.4%) 1 (4.2%) 0 (0%) 0 (0%) 0 (0%)
Ketamine Sedation 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
NO2 Sedation 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)
Sucrose Sedation 1 (0.4%) 0 (0%) 0 (0%) 1 (1.8%) 0 (0%)
Type of Airway




    ETT 172 (70%) 15 (63%) 37 (77%) 43 (77%) 77 (65%)
    LMA 38 (15%) 2 (8.3%) 4 (8.3%) 5 (8.9%) 27 (23%)
    Anaesthetic Face Mask 4 (1.6%) 1 (4.2%) 0 (0%) 1 (1.8%) 2 (1.7%)
    HFNP 8 (3.3%) 1 (4.2%) 3 (6.3%) 1 (1.8%) 3 (2.5%)
    Hudson Mask 2 (0.8%) 0 (0%) 1 (2.1%) 0 (0%) 1 (0.8%)
    LFNP 11 (4.5%) 3 (13%) 2 (4.2%) 4 (7.1%) 2 (1.7%)
    Guedel 2 (0.8%) 0 (0%) 0 (0%) 1 (1.8%) 1 (0.8%)
    Chin Support 1 (0.4%) 0 (0%) 0 (0%) 0 (0%) 1 (0.8%)
    None 8 (3.3%) 2 (8.3%) 1 (2.1%) 1 (1.8%) 4 (3.4%)
1

n; n (%)

2.4 Anaesthetic Complications

2.5 Post-Operative Management

2.6 Post-Operative Adverse Events